High-precision positioners are an enabling component of many scientific and industrial instruments. Such instruments are widely used in a variety of fields, for example, in optical microscopy and spectroscopy, electron microscopy, scanning probe microscopy, nanotechnology, wafer inspection, micro assembly, optical fiber alignment methods in optoelectronics, and many others. To be able to move objects with nano-scale accuracy, one needs to measure the position of an object with even more precision. Dimensional position encoders are known; for three-dimensional position encoding, one such encoder is needed for each degree of motion.
U.S. Pat. No. 6,130,427 to Park et al. disclose an optical setup for measuring xyz coordinates of a movable cartridge carrying a scanning microscope probe. The cartridge is affixed to the top of a piezoelectric tube having multiple electrodes. Application of appropriate voltages across the electrodes produces displacement in the plane of the top surface (xy) and along the axis of the tube (z). In this prior art, displacements x and y of the cartridge are measured by the spot where a probing beam of light impinges on a 4-quadrant photodetector positioned in the xy plane. Axial displacement z is measured separately requiring two additional bi-cell photodetectors positioned along a z axis, and two additional probing beams of light. The resulting setup is quite complex and difficult to manufacture, as it requires a complicated alignment.